A liquid crystal display device is configured by a liquid crystal layer, a backlight device, and the like. The backlight device in such a liquid crystal display device includes a device using white light. Moreover, a recent backlight device uses an LED (light-emitting diode) as a light source thereof.
When the LED is used as the light source of the backlight device of the liquid crystal display device, the LED is driven by, for example, PWM (Pulse Width Modulation) (for example, refer to Patent Document 1). In the PWM drive, a pulse width to be input to the LED is controlled to control brightness of the LED, that is, brightness of the backlight to be used as the light source.
Moreover, an afterimage time of the LED is shorter than that of a fluorescent tube conventionally used as the light source. Therefore, in a lighting device using the LED, standards for preventing a feeling of unwellness or the like of a user due to flicker of light output are defined (for example, refer to Non-Patent Document 1). In the standards, a technical criterion that the user does not feel flicker of light output is defined. In Non-Patent Document 1, it is described that one having a repetition frequency of 100 [Hz] or higher and no missing part in the light output, or one having a repetition frequency of 500 [Hz] or higher, is construed as “no sense of flicker”. Accordingly, in the backlight device using the LED, when control by the drive of the PWM (hereinafter, referred to as “PWM drive”) is executed, if the repetition frequency is low, it is considered that flicker similar to that of an LED lighting device occurs. Therefore, in order to reduce flicker in the backlight device using the LED, the repetition frequency in the PWM drive needs to be increased.